Final answer:
The most dramatic decline in air pollution in the U.S. from 1970 to 1990 was due to reductions in vehicle emissions and pollutants from coal-fired power plants, facilitated by the Clean Air Act of 1970 which required a 90 percent reduction in vehicle emissions.
Step-by-step explanation:
The Most Dramatic Decline in Air Pollution from 1970 to 1990
The type of air pollution that saw the most dramatic decline in the United States during the period from 1970 to 1990 was attributed to reductions in emissions from vehicles and coal-fired power plants. Policies such as the stricter Clean Air Act signed by President Nixon in 1970 played a significant role. This act mandated new pollution standards for industries and required a 90 percent reduction in vehicle emissions, which was primarily achieved through the adoption of catalytic converters. Furthermore, the technology to scrub sulfur and other pollutants from coal plant emissions helped reduce the environmental damage from acid rain.
While carbon dioxide (CO2) emissions reductions are noted from 2007 to 2012, it's important to remember that substantial improvements in air quality and a decline in specific air pollutants were achieved much earlier, following the 1970 Clean Air Act and other measures. The 1970s and 1980s saw a major decrease in smog and pollutants that were common in the 1950s and 1960s, largely thanks to these environmental policies.